In view of numerous shortfalls of the Wireless Personal Area Network (wPAN) Media Access Control (MAC) protocol of the IEEE standard 802.15.3, which is based on a centralized-control protocol, the Multi-Band Orthogonal Frequency-Division Multiplexing (OFDM) Alliance (MBOA) group started a MBOA MAC subgroup. The MBOA MAC is based on a distributed protocol rather than a centralized-controlled protocol as used in the IEEE 802.15.3 MAC. In order for every wireless device to be able to form a network by itself, each device is typically required to beacon in a distributed manner in a superframe.
The beginning of the superframe is typically reserved for beacon transmission. The number of Media Access Slots (MAS) used for beaconing purposes is defined as a Beacon Period (BP) and the remainder of the MAS in the superframe are used for data transfer. The BP is typically dynamic in length and consists of a dynamic number of beacon slots, which extends across up to 20 contiguous MAS. A Beacon Group (BG) is defined as a group of devices which synchronize their beacon transmissions within the same group of MAS in the superframe and which identify these MAS as their BP. The BP expands when new devices join the BG and contracts when devices leave the BG.
Since coexistence of independent BGs typically poses a problem In relation to decentralized network implementation, under the MBOA MAC standard, when two or more BGs are within range of each other, devices of the BGs coalesce to a single BP. The BP of one of the BGs is therefore expanded to accommodate the beacon transmissions of the joining devices from other BGs. However, in the MBOA MAC v0.6 draft specification, there is currently no defined method to select which BG's BP should remain unchanged and which BG should synchronise to join the unchanged BG. When two or more BGs merge, the BG that expands its BP to accommodate devices from other BGs is termed as the Leader BG (LBG) while the remainder of the BGs that coalesce into the LBG are termed as Follower BGs (FBGs).
Devices in a FBG have to change their beacon slots (BS) as well as reschedule or re-negotiate their other data transfer reservations, if any, when the FBGs merge into the LBG. For best device performance considerations, no device would voluntarily choose to be the one to merge into another BG. Therefore, a set of rules is needed so that every device can decide during BG merging whether it should continue beaconing in its current BG or join another BG based on the rules. The rules should enable every device to be able to determine whether its BG is the LBG or a FBG when it comes into range of one or more BGs.
A LBG selection method should ensure fairness. For selection to be fair, the least network disruption should be incurred When considering a selection based on the least impact on existing network topology, the selection can be defined such that a smaller BG always joins a bigger BG so that fewer devices are affected by the merging. Thus, during BG merging, the BG with the most number of member devices-assumes the LBG role and the rest of the BGs, being FBGs, coalesce into the LBG. However, one problem with this selection method is that BG size is typically a temporary value which is subjected to unpredictable changes in every superframe since devices can enter or leave at any time in a WPAN. Another problem is that the total number of devices in a BG is typically not propagated throughout the entire BG. This is true for WPANs where devices can typically only see other devices that are up to 2 hops away.
When considering a selection based on the least impact on ongoing data transfer, in the context of MBOA MAC, the selection is defined such that a BG with comparatively lesser existing data transfer reservations joins a BG with comparatively more existing data transfer reservations. One problem associated with this selection method is that a typical data transfer reservation count is even more temporary than BG size, even when BG size remains unchanged. Another problem is that the total data transfer reservation count is typically not propagated throughout the BG.
In existing attempts to counter the problems of local/neighbouring selection criteria that are based on temporary values as mentioned above, globally consistent selection criteria can be used. One such criteria is network time, which is typically the running clock value in every device. However, one problem with selecting a LBG using network time is that high accuracy clocks are typically required to ensure that all devices in the same BG report the same network time in every superframe.
Another globally consistent selection criteria that has been considered is the usage of the MAC address of each Device ID (DEVID) since the MAC address is consistent and fixed throughout network operation. However, a problem with this selection criteria is that the selection is typically consistently unfair to devices with less advantageous MAC addresses or DEVIDs in terms of the selection criteria used, such as alphabetical order, etc.
Hence, there exists a need to provide a method or system of Beacon Group merging to address one or more of the above problems.